A MEMS (Micro Electro Mechanical System) Element is a device often operating as a switchable capacitor on a substrate and having a first and a second electrode. A first electrode is configured as a moveable beam that is located above the other electrode which is in a fixed position on a substrate. The two planar electrodes are separated by a cavity. The spacing between the two planar electrodes is variable by an external force exerted on the moveable beam.
Typically, the cavity between the two planar electrodes is manufactured by the use of a sacrificial layer. On the planar electrode on the substrate a first layer is deposited as sacrificial layer and is patterned so as to form a sacrificial body. On the sacrificial body a second layer is deposited. The second layer is patterned to form the body of the moveable beam. Next, the sacrificial body is removed between the moveable beam and the planar electrode on the substrate so as to form the cavity.
A disadvantage of this method is that the step coverage of the second layer on the sacrificial body is relatively poor. Typically, the thickness of the second layer on the lateral edges of the sacrificial body is reduced in comparison to the thickness of the second layer on the substrate and/or on the sacrificial body.
In an example of a switchable capacitor, a typical thickness of the sacrificial layer may be about 3 micrometer while the thickness of the second layer may be about 5 micrometer. At the lateral edges of the sacrificial body the thickness of the second layer may be reduced to about 2-3 micrometer.
As a result, the variation of the thickness of the moveable beam leads to a large spread of the mechanical properties of the beam and of the MEMS device that comprises the switchable capacitor.